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I was wondering if there is a way of introducing intertext within a split environment. I would like to be able to write something like


\documentclass{article}[10pt]
\usepackage{amsmath, hyperref, amsfonts}
\providecommand{\abs}[1]{\left|#1\right|} 
\begin{document}
\begin{align}
\begin{split}
\mathbb{P}\left[\abs{X - \mu} \geq h\sigma\right] &\leq \dfrac{\left[f(\abs{X - \mu})\right]}{f(h\sigma)}
\intertext{Letting $f(\cdot) = (\cdot)^2$,}
\mathbb{P}\left[\abs{X - \mu} \geq h\sigma\right] &\geq 1 - \dfrac{\sigma^2}{h^2\sigma^2}
\end{split}
\end{align}
\end{document}

so that the whole thing, including the text in the middle, gets one number centered on the whole align environment.

Obviously, this is a debatable way of numbering equations, but for very short intertexts this is okay, IMHO.

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1  
Welcome to TeX.sx! Please always provide complete minimal working example (MWE), i.e. with a minimal preamble and the document environment. –  Martin Scharrer Oct 29 '11 at 17:22
    
Apart from the fact that you don't say where you want to align your equations, putting a text in between those two equations will print the equation number vertically aligned with the text: not very useful for your reader. –  egreg Oct 29 '11 at 17:41
    
@egreg Not had enough coffee this morning clearly. Fixed the alignment. Regarding the vertical alignment with the text, this is a dummy example and I am thinking of much larger equation sets with possibly one short line of intertext. –  fg nu Oct 29 '11 at 17:42

1 Answer 1

up vote 3 down vote accepted

It's not possible to use \intertext inside a split environment, because it builds a "subalignment" which is treated as a unique block. But you can fool LaTeX by leaving some space for the text and inserting it after the split:

\begin{align}
a&=b\\
\begin{split}
c&=d\\[\baselineskip]
e&=f
\end{split}\\[-\jot]
\noalign{\noindent\raisebox{2\baselineskip}[0pt][0pt]{Some text}}
g&=h
\end{align}

or

\begin{align}
a&=b\\[-\jot]
\noalign{\noindent\raisebox{-2.5\baselineskip}[0pt][0pt]{Some text}}
\begin{split}
c&=d\\[\baselineskip]
e&=f
\end{split}\\
g&=h
\end{align}

but for this to work you need an equation before or after the split.

However, your reader will have a hard time trying to figure out what the number refers to.

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+1 especially for the final sentence. Unless you were to encase the entire block of displayed-math-plus-text with a left or right brace, to group the things being numbered, having some equation number floating vaguely to the side is not really constructive. –  Niel de Beaudrap Oct 29 '11 at 20:40
    
egreg:Thanks, but clearly I need to change my strategy of writing what I am writing. @NieldeBeaudrap It is tedious to repeat allowances I have already made in my original question. I am aware of what effects this presentation might have and have made a choice on balance knowing my needs. –  fg nu Oct 31 '11 at 18:41

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